This grant in the Organic and Macromolecular Chemistry Program provides support for the research of Dr. Robert Pascal, Jr., Princeton University. The work is focused on the structures of molecules in which two relatively unreactive molecular entities are forced to be very close together. Groups of atoms which are forced in this way to occupy a limited space have unusual behavior, both in terms of their chemical reactivity and their physical properties. In one class of target molecules, methine, amine, and ammonium groups will be pressed near the periphery of the pi electron clouds of aromatic rings; in a second class these same groups will be projected toward the center of the rings. In the first case, the substituents on the "target" phenyl groups will be varied to produce aromatic rings which are relatively electron-rich or electron-deficient. The extent of interaction of the functional groups with the ring should vary with this electronic substitution. In the second class of compounds, increased interactions will be achieved not by the variation of aromatic ring substituents, but by synthesizing a series of compounds in which the distance between the functional group and ring is systematically reduced. By balancing the forces due to intramolecular strain in these compounds with the degree of nucleophilicity or electrophilicity of the ring, structures may be observed with partial bonding between these groups. Such structures should be interpretable as analogs of transition states (which are not themselves observable) in the nucleophilic and electrophilic substitution reactions of aromatic compounds.
